[time-nuts] "The Penultimate HP5065 A15"

[Bob kb8tq]

Hi

> On Aug 4, 2020, at 2:49 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> 
> --------
> Bob kb8tq writes:
> 
>>>> I would go for the LTZ1000 if you can. The LM399 has gone out of
>>>> fashion for a reason: [...]
>>> 
>>> Yes, I know, being also a volt-nut :-)
>>> 
>>> Problem is, the A15 PCB isn't all that big, and if you want
>>> cooling fins on two TO220's, a lot if it just got occupied.
> 
> Just to follow up on the LTZ1000, this seems to be the smallest
> non-SMD implementation of it:
> 
> 	https://github.com/pepaslabs/px-ref/tree/master/kicad/releases/v2.4.1
> 
> That's a quarter of the A15 acreage, and more than I think is
> warranted.

You have already looked at the lamp supply sensitivity and the C-field.
I don’t see any reason to go overly nutty with super references. You have
a whole bunch of interesting ground issues and have various modules fed
*through* the TED. 

> 
>> Unless you are running internal batteries, the battery charger board 
>> (as you have noted) is pretty much empty. For most of us, the 100 KHz
>> and 1 MHz boards also are not very useful. They *could* be converted 
>> to other tasks. 
> 
> One of the premises for my current mucking about with kicad was to
> make a plug-compatible A15, so that A/B testing would be easy,
> both for me and for anybody else who wants to tag along.
> 
>> There is a lot of space on the chassis for the batteries, the 1 pps 
>> divider and the clock. 1 pps is much easier to do today than it once was.
>> Clock may or may not be a useful option. Again, a lot of space to 
>> expand this or that into. 
> 
> Indeed.
> 
> I've kept & even renovated the LED clock, because it was there, but
> I used the chance to get rid of the entire divider-chain:
> 
> 	http://phk.freebsd.dk/hacks/HP5065A/20160112_working_clock/
> 
>>> BTW: I found a simple solution to this:  I use the existing
>>> chassis-mount NPN transistor as a pre-regulator, so the LDO's will
>>> never see more voltage than they need to for regulation.
> 
>> Pre-reg might also feed the heater circuits. One *could* do a pre-reg on the
>> battery charger board. There pretty much has to be some impact to having
>> the voltage to the heaters un-regulated ….
> 
> As I said above, I'd like the A15 to be plug compatible if possible.
> 
> Stabilizing the voltage for the heaters helped when I tried it,
> but it is not obvious if this is due to misalignment or intrinsic
> in the thermostatic regulators.

Using OCXO’s as a reference, the supply voltage does indeed get in and mess with
the set point. Less so on an external pass transistor design (like the 5065) than on an
“all on the oven” approach. 

My though would be to put the pre-regulator in the A2 / A16 slot. That way it’s not
soaking up any of the A15 board space. It also would make it fairly easy to swap 
things one at a time. 

In a design where you already have a switcher feeding the A15 (and the heaters), 
I doubt there would be a significant advantage to a pre-regulator. 

Bob


> 
> I don't think stabilization on the LM399 level is required, but more
> stable than the grid voltage would be good.
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.